| With the rapid development of the social economy and the improvement of people’s living standards,citrus must meet the output requirements and meet consumers’increasing quality requirements.Irrigation and fertilization are important factors that affect the growth and development of citrus,and they are also the regulators of citrus yield and quality.At present,there is a phenomenon of unreasonable water and fertilizer application due to improper field management methods in citrus production in Sichuan Province,which will not only affect the yield and fruit quality of citrus,but also cause waste of resources and environmental pollution.The law of response and the determination of a scientific and reasonable integrated management model of water and fertilizer are of great significance for saving resources,improving quality and increasing income,and environmental protection.In this paper,8-year-old"unbeknownst fire"citrus was used as the test material to carry out the experimental study on the integration of water and fertilizer under low-pressure drip irrigation.Two irrigation levels(W60%and W80%,respectively,means60%and 80%of CK)were set at the stage of flowering(Ⅰ),young fruit(Ⅱ),fruit expansion(Ⅲ)and fruit maturity(Ⅳ).Three fertilization levels(F55%,F70%and F85%,respectively,means 55%,70%and 85%of CK)were set up.This paper analyzed the changes of water consumption,yield and fruit quality of citrus,constructed water-fertilizer-yield and water-fertilizer-quality models of citrus,and proposed the optimal water and fertilizer management model for citrus under low pressure drip irrigation.The main results are as follows:(1)The water consumption intensity of citrus under different water and fertilizer treatments showed a trend of first increasing and then decreasing with the growth period,and the water consumption intensity in each growth period was in order of stage III>IV>II>I.And water had a greater impact on the water consumption intensity than nutrients.Water and fertilizer treatment at different growth stages had significant effects on citrus yield,among whichⅠ-W60%F85%was the highest,Ⅲ-W60%F55%was the lowest.(2)In the first stage of water and fertilizer deficit,under the same irrigation level,the single fruit weight and V_c of different treatments showed the rule of F85%>F70%>F55%.Under the same fertilization level,the single fruit weight,V_c,soluble solids and titratable acid of different treatments,solid acid ratio,soluble sugar,and color have no obvious rules.In stageⅡwater and fertilizer shortage,under the same irrigation level,the V_c,soluble solids and soluble sugar content of different treatments increased with the increase of the amount of fertilization.Under the same fertilization level,the single fruit weight,V_c and soluble solids of different treatments W80%>W60%law.In the third stage,under the same irrigation level,the single fruit weight,V_c,soluble solids and soluble sugar showed the highest F85%,followed by F70%,and the lowest F55%.Under the same fertilization level,the single fruit weight and V_c content of different treatments varied with irrigation the amount increases.In stageⅣ,under the same irrigation condition,the contents of V_c,soluble solids,soluble sugar and titratable acidity increased with the increase of the amount of fertilization.Under the same fertilization condition,the higher the irrigation amount,the greater the single fruit weight,the soluble solids and the titratable acid content the higher.Fruit expansion and ripening are the growth periods which have great influence on fruit chroma.The deficiency of water and fertilizer in each growth period will reduce the content of titratable acid and affect the flavor of citrus.(3)In the first stage of water and fertilizer deficit,under the same irrigation level,the syringate content of different treatments was F70%>F85%>F55%.Under the same fertilization level,the content of vanillic acid,syringate,rutin,vanillin was W60%>W80%.In stageⅡwater and fertilizer shortage,the rutin content of different treatments increased with the increase of fertilizer application at the same irrigation level.At the same fertilization level,vanillic acid,syringate,rutin and rutin showed a rule of W60%>W80%.In stageⅢwater and fertilizer shortage,at the same irrigation level,rutin of different treatments showed the rule of F85%>F70%>F55%.At the same fertilization level,vanillic acid,rutin and vanillin showed W60%>W80%.In stageⅣwater and fertilizer shortage,at the same irrigation level,the content of rutin,rutin and vanillin in different treatments increased with the increase of fertilization,at the same fertilization level while the content of rutin and vanillin decreased with the increase of irrigation water.In addition,the content of vanillin and rutin were increased by water and fertilizer deficit in each growth period of citrus,and decreased by water and fertilizer deficit in stage II,but increased by water and fertilizer deficit in stage III and IV.(4)Analyze the water-fertilizer-yield model using 3 years of measured data and find that the sensitivity of citrus yield water and fertilizer deficit was stageⅢ>stageⅠ>stageⅡ>stageⅣ.And the Minhas model is recommended simulate citrus water-fertilizer-yield relationship.Using 2 years of measured quality data for water-fertilizer-quality model analysis,it is found that V_c,titratable acid,soluble solids,solid acid ratio,soluble sugar,chroma were more sensitive to stage III and stage IV,single fruit weight was more sensitive to stage III;meanwhile,it was found that the the Q＿Rao model is more applicable.It is recommended to use the Q＿Rao model to simulate the citrus water and fertilizer and fruit weight,V_c,soluble solids,titratable acid,solid acid ratio,soluble sugar and chroma relationship.(5)The optimal water and fertilizer management model for citrus under rain shelter and low-pressure drip irrigation is:the irrigation quotas of the first stage to the fourth stage are 7.7 mm,13.2 mm,21.9 mm,12.6 mm,and the irrigation frequencies are 10 d,8-10 d,7d,10-11 d;The fertilization quotas of stage I to stage IV are 382.5 kg/hm~2,829.5 kg/hm~2,1467.0 kg/hm~2,382.5 kg/hm~2,and the frequency of fertilization is 15 d.Irrigation and fertilization start from the beginning of April,irrigation lasts for the whole growth period,and the fertilization time ends at the end of November.The optimal water and fertilizer management model for field citrus under low-pressure drip irrigation is:water-rich year(25%),8 times of irrigation in stageⅣ;flat water year(50%),9 times of irrigation in stageⅣ;dry water in the year(75%),the stage III irrigation was twice,the stage IV irrigation was 10 times;in the dry year(85%),the stage III irrigation was 4 times,the stage IV irrigation 10 times;in special drought years(95%),irrigation was carried out 5 times in the third stage,10 times in the fourth stage.Fertilization time:from the beginning of April,fertilize every 15 days,and cut off by the end of November. |
